mtn: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/mtn - from package: monotone

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/mtn - from package: monotone

You may install the required package with command apt-get install {package}

Error in other languages:
mtn: bevel nie gevind nie
mtn: comandă negăsită
mtn: comando não encontrado
mtn: commande introuvable
mtn: command not found
mtn: käsku ei ole
mtn: không tìm thấy lệnh
mtn: komanda nerasta
mtn: Kommando nicht gefunden.
mtn: kommandot finns inte
mtn: komut yok
mtn: nie znaleziono polecenia
mtn: níor aimsíodh an t-ordú
mtn: no se encontró la orden
mtn: no s'ha trobat l'ordre
mtn: opdracht niet gevonden
mtn: parancs nem található
mtn: perintah tidak ditemukan
mtn: príkaz nenájdený
mtn: příkaz nenalezen
mtn: команда не найдена
mtn: командата не е открита
mtn: 命令找不到
mtn: コマンドが見つかりません